Lower back pain may oftentimes be attributed to the rupture or degeneration of lumbar intervertebral discs due to degenerative disk disease, isthmic spondylolisthesis, post laminectomy syndrome, deformative disorders, trauma, tumors and the like. This pain may result from the compression of spinal nerve roots by damaged discs between the vertebra, the collapse of the disc, and the resulting adverse effects of bearing the majority of the patient's body weight through a damaged unstable vertebral joint. To remedy this, spinal implants may be inserted between the vertebral bodies to restore the joint to its previous height and stabilize the motion at that spinal segment.
Numerous materials have been described for the preparation of spinal implants that possess desired mechanical and biological properties. Polyetheretherketone (PEEK) is a thermoplastic with excellent mechanical properties, including a Young's modulus of about 3.6 GPa and a tensile strength of about 100 MPa. PEEK is partially crystalline, melts at about 334° C., and is resistant to thermal degradation. PEEK is a biomaterial used in medical implants. For example, PEEK can be molded into preselected shapes that possess desirable load-bearing properties. But such materials are not bioactive, osteoproductive, or osteoconductive. Bioactive glasses and glass-ceramics are characterized by their ability to form a direct bond with bone. A material based on the PEEK polymer, or similar types of polymers of the PEEK family that includes the bone-bonding properties of a bioactive glass would be desirable.
The prior art does not provide a material or a method of making the material which combines a biocompatible polymer such as PEEK with a bioactive glass having a particle size larger than one micron. Furthermore, the art does not disclose a material or method of making a bioactive implant material which combines PEEK and bioactive glass and which has the appropriate structural and mechanical properties to withstand the stresses necessary for use in spinal implants.
A combination of polymers including PEEK and combeite glass-ceramic, a bioactive glass, has generally been described in U.S. Pat. Nos. 5,681,872; 5,914,356; and 6,987,136; each of which is assigned to the assignee of the present invention and is incorporated herein by reference in its entirety. It has been discovered, however, that conventional methods of combining PEEK and combeite, for example, combination using a twin screw extruder, result in a reaction between the PEEK and the combeite glass-ceramic forming a material having properties that inhibit extruder functioning. In some instances, the high reactivity of such bioactive materials with the polymers makes combining bioactive materials, such as glass, ceramics, and glass-ceramics, with PEEK, or similar polymers of the PEEK family, a challenge using conventional processing. What is needed, therefore, is a method of preparing a composite of PEEK and bioactive glass.